Use of Affectations in planing calculation

Affectation rate is taken into account... on a weekly basis.
It is considered that if a resource is affected 50% on P1 and 50% on P2, it should not work half days on each, but half weeks on each.
It means planning will set 2,5 days on P1 then 2,5 daus on P2.
Try and change your effort to 5, you'll see what I mean.

If you want a daily basis restriction, use assignement rate at 50%.